For many years voice telephone service was implemented over a circuit switched network commonly known as the public switched telephone network (PSTN) and controlled by a local telephone service provider. In such systems, the analog electrical signals representing the conversation are transmitted between the two telephone handsets on a dedicated twisted-pair-copper-wire circuit. More specifically, each of the two endpoint telephones is coupled to a local switching station by a dedicated pair of copper wires known as a subscriber loop. The two switching stations are connected by a trunk line network comprising multiple copper wire pairs. When a telephone call is placed, the circuit is completed by dynamically coupling each subscriber loop to a dedicated pair of copper wires in the trunk line network that completes the circuit between the two local switching stations.
A key advantage of a circuit switched network is that a dedicated circuit is continually connected between the two endpoints and capable of carrying information at a fixed rate (in this case, a voice audio signal) for the entire duration of the call. A disadvantage of a circuit switched network is the size and expense of trunk lines between switching stations that must be large enough to provide a dedicated pair of copper wires for each circuit.
More recently the trunk lines between switching stations have been replaced with fiber optic cables. A computing device digitizes the analog signals of each circuit and formats the digitized data into frames such that multiple conversations can be transmitted simultaneously on the same fiber utilizing a time division protocol. At the receiving end, a computing device reforms the analog signals of each circuit for coupling to the copper wires of the subscriber loop. Fiber optic cable increases trunk line capacity between switching stations and simultaneously reduces trunk line cost.
Historically, the technology used for provision of cable television service was a separate and distinct technology from the PSTN. Cable television signals were analog signals broadcast over a multi-drop coaxial cable network. This arrangement seemed to work well, because the trunk line and subscriber loop architecture of the PSTN was conducive to end to end voice communications that required a dedicated circuit between the two endpoints while the mutli-drop architecture of the coaxial cable network was conducive to simultaneously broadcasting a television signal from a single source to multiple customers.
Advances in packet switched communication technologies, audio compression technologies, and network capacity have made it possible for telephone calls, Internet connections, and digital cable TV programming (all of which require a dedicated end-to-end communication channel) to be provided using end-to-end logical channels over a multi-drop network utilizing a packet-switched communication protocol. A Hybrid Fiber Cable (HFC) network that includes fiber optic trunk lines interconnecting digital routers which limit the multi-drop architecture to only those portions of the network that interconnect to a limited number of customers is most conducive to providing end-to-end communication channels utilizing a packet-switched communication protocol.
To enable digital telephone service over an HFC network to interoperate with a customer's traditional PSTN telephone equipment a customer gateway, at the customer's facility, performs applicable conversion to communicate over the HFC network with a “soft switch” and emulates an analog PSTN line for communication over a twisted pair copper wire network at the customer's premises. Early gateways used a committed bit rate (CBR) system wherein a dedicated time slot over the HFC network is kept open between the customer gateway and the service provider gateway and used continuously for transferring frames that, when decompressed, represent the analog subscriber loop. The time slot provides assurance of adequate bandwidth for the transmission of each frame such that it may be received on a timely basis for reproducing the analog signals at the receiving system. The time slots remain open regardless of whether a call is in progress and all call signaling and media communication are “in-band” on the subscriber loop.
More recently a digital protocol known as DOCSIS has been implemented on HFC networks as an underlying protocol that would support all of digital telephone service, digital cable television services, and Internet connection services. DOCSIS uses a dynamic quality of service model (DQOS) between a DOCSIS cable modem and a cable modem termination server (CMTS) that establishes a dedicated time slot for a telephone call only for a period of time during which the call is in progress. The advantage of the DOCSIS system over the CBR system is an overall increase in bandwidth as the system is not idle during time slots when no call is in progress.
In a DOCSIS network, a device known as an embedded multi-media terminal adapter (MTA) interfaces with the DOCSIS network and emulates a PSTN subscriber loop on the twisted pair network at the customer's premises. The embedded MTA may request a dedicated time slot from the CMTS upon initiating a telephone call, receive an assigned time slot in an acknowledgement from the CMTS, and thereafter format frames representing the telephone call to fit the period of the time slot and exchange the frames over the HFC network during the time slot. A problem with use of an embedded MTA is that it obsoletes current cable modems that do not include embedded MTA capability.
A device known as a stand alone MTA also has been contemplated. The stand alone MTA will connect to a known DOCSIS cable modem that does not include embedded MTA capability. A problem with the stand alone MTA architecture is that the MTA can not communicate directly with the cable modem—the cable modem operates only as a conduit routing frames directly between the MTA and the CMTS.
As such, reservation of a time slot by the MTA uses system known as RSVP. RSVP provides for the MTA to request a time slot from the CMTS. The CMTS verifies the authenticity of the request from the soft switch and provides the time slot information to both the cable modem and to the MTA.
A need exists for a stand alone MTA system that enables direct communication between the cable modem and the MTA and, more specifically, enables the MTA to control the dynamic quality of service function of the cable modem.